Electrosurgical systems have been used for a number of years in surgical procedures to cut and shape tissue at the surgical site while minimizing blood loss. As illustrated in the example of FIG. 1, a typical electrosurgical system includes an electrosurgical probe 12 (hereafter referred to simply as “probe”) and a control console 14. The probe 12 generally comprises an elongated shaft 16 with a handle 18 at one end and a tip 20 at the opposite end. A single active electrode 19 is provided at the tip 20 if the probe 12 is of a “monopolar” design. Conversely, the probe 12 may be provided with both an active electrode 19 and return electrode 21 at the tip 20 if the probe is “bipolar” in design. The probe 12 connects to controller 14 by means of a detachable cable 22. The current for energizing the probe 12 comes from control console 14. When actuated, the control console 14 generates a power signal suitable for applying across the electrode(s) located at the tip 20 of the probe 12. Specifically, current generated by the control console 14 travels through the detachable cable 22 and down the shaft 16 to tip 20, where the current subsequently energizes the active electrode 19. If the probe 12 is monopolar, the current will depart from tip 20 and travel through the patient's body to a remote return electrode attached thereto. If the probe 12 is bipolar, the current will primarily pass from the active electrode 19 located at tip 20 to the return electrode 21, also located at tip 20, and subsequently back up the shaft 16 and through the detachable cable 22 to the control console 14.
Configuration of the control console 14 is carried out by means of an interface 15, while actuation and control of the probe 12 by the surgeon is accomplished by one or more switches 23 on the probe 12. One or more remote controllers, such as, for example, a footswitch 24 having additional switches 26 and 28, respectively, may also be utilized to provide the surgeon with greater control over the system 10. In response to the surgeon's manipulation of the various switches on the probe 12 and/or remote controller 24, the control console 14 generates and applies either a low power signal or high power signal to probe 12. As will be discussed in greater detail below, application of a low power signal to probe 12 results in the coagulation of the tissue adjacent the tip 20. In contrast, application of a high energy signal to probe 12 results in tissue ablation.
Although they have arguably revolutionized modern surgical practice, traditional electrosurgical systems continue to exhibit various deficiencies that make them difficult to use. For instance, there are frequently other types of instruments being utilized at or near the surgical site area of the patient's body making up the surgical site. These additional instruments, which can range from simple manipulators to sophisticated endoscopes, are often constructed from or contain electrically conductive material. As such, extra care must be taken when utilizing an electrosurgical probe at the surgical site so as to avoid having the probe coming in close proximity to, or in contact with another instrument, which can result in an arc of energy or increase in current that travels to the other instrument and transfers electrical current thereto.
In addition to the above deficiencies, electrosurgical systems can also be difficult to control. For instance, regulations frequently imposed on electrosurgical systems mandate that they not operate at power levels that exceed a predefined limit. However, maintaining an electrosurgical system in an ablative operating state can potentially result in the system operating at power levels that exceed the mandated maximum level. To assure that they operate at acceptable power levels, traditional electrosurgical systems are usually configured to monitor power levels, and in response to the detection of an excessive power level, modify the amount of voltage and/or current that they generate and use to drive their probe. However, such modifications to the voltage and/or current levels can result in operating instabilities that decrease the effectiveness of the probe.
To detect abnormal operating conditions that could potentially cause undesirable increases in power levels, traditional electrosurgical systems monitor certain operating parameters and calculate the electrical impedance or load that is encountered by the system and which represents the conditions existing at the tip of the probe. However, due to inherent delays in the process, the determination of impedance is found to not always be the most effective means of detecting undesirable conditions.